Electrolytic eluent generator

ABSTRACT

An acid or base is generated in an aqueous solution by the steps of: (a) providing a source of first ions adjacent an aqueous liquid in a first acid or base generation zone, separated by a first barrier (e.g., anion exchange membrane) substantially preventing liquid flow and transporting ions only of the same charge as said first ions, (b) providing a source of second ions of opposite charge adjacent an aqueous liquid in a second acid or base generation zone, separated by a second barrier transporting ions only of the same charge as the second ions, and (c) transporting ions across the first barrier by applying an electrical potential through said first and second zones to generate an acid-containing aqueous solution in one of said first or second zones and a base-containing aqueous solution in the other one which may be combined to form a salt. Also, electrolytic apparatus for performing the above method.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 10/241,361 filed Sep. 11, 2002

BACKGROUND OF THE INVENTION

Ion chromatography and other forms of liquid chromatography are widelyused analytical techniques for determination of ionic analytes. Dilutesolutions of acids, bases, and salts such as sodium carbonate and sodiumbicarbonate are used as eluents in the ion chromatographic separations.Traditionally, these eluents are prepared off-line by dilution withreagent-grade chemicals. Off-line preparation of chromatographic eluentscan be tedious and prone to operator errors, and often introducescontaminants. For example, dilute NaOH solutions, widely used as eluentsin the ion chromatographic separation of anions, are easily contaminatedby carbonate. The preparation of carbonate-free NaOH eluents isdifficult because carbonate can be introduced as an impurity from thereagents or by adsorption of carbon dioxide from air. The presence ofcarbonate in NaOH eluents often compromises the performance of an ionchromatographic method, and can cause an undesirable chromatographicbaseline drift during the hydroxide gradient and even irreproducibleretention times of target analytes. Therefore, there is a general needfor convenient sources of high purity acid, base, or salt for use aseluents in the ion chromatographic separations.

U.S. Pat. No. 5,045,204 describes an impure acid or base is purified inan eluent generator while flowing through a source channel along apermselective ion exchange membrane which separates the source channelfrom a product channel. The membrane allows selective passage of cationsor anions. An electrical potential is applied between the source channeland the product channel so that the anions or cations of the acid orbase pass from the former to the latter to generate therein a base oracid with electrolytically generated hydroxide ions or hydronium ions,respectively. This system requires an aqueous stream of acid or base asa starting source or reservoir.

U.S. Pat. No. 6,036,921 and U.S. Pat. No. 6,225,129 describeelectrolytic devices that can be used to generate high purity acid andbase solutions by using water as the carrier. Using these devices, highpurity, contaminant-free acid or base solutions are automaticallygenerated on-line for use as eluents in chromatographic separations.These devices simplify gradient separations that can now be performedusing electrical current gradients with minimal delay instead of using aconventional mechanical gradient pump.

Dilute solutions of salts such as sodium carbonate and sodiumbicarbonate are often used as eluents in ion chromatographicseparations. One object of the present invention is to develop methodsand devices for generating such high purity salt solutions using wateras a carrier.

SUMMARY OF THE INVENTION

In one embodiment of the invention, an acid or base is generated in anaqueous solution by the steps of:

(a) providing a source of first ions adjacent an aqueous liquid in afirst acid or base generation zone, said first ion source and first zonebeing separated by a first barrier substantially preventing liquid flowand transporting ions only of the same charge as said first ions,

(b) providing a source of second ions of opposite charge to said firstions adjacent an aqueous liquid in a second acid or base generationzone, said second ion source and second zone being separated by a secondbarrier substantially preventing liquid flow and transporting ions onlyof the same charge as said second ions, and

(c) transporting ions of a first charge, positive or negative, acrosssaid first barrier by applying an electrical potential through saidfirst zone to electrically charge the same with a charge opposite tosaid first charge and applying an electrical potential through saidsecond zone to electrically charge the same with a charge opposite tothe charge of said first zone so that hydroxide ions are generated inone of said first or second zones and hydronium ions are generated inthe other of said first and second zones and ions of opposite charge tothe electrical charges of said first and second zones, respectively, aretransported across said first and second barriers to combine with saidhydroxide or hydronium ions in said first and second zones to generatean acid-containing aqueous solution in one of said first or second zonesand a base-containing aqueous solution in the other one.

In another embodiment, an acid or base is generated in an aqueoussolution by a method comprising the steps of:

(a) providing a source of first ions adjacent an aqueous liquid in afirst zone comprising ion exchange medium having exchangeable ions ofthe same charge as said first ions, said first ion source and first zonebeing separated by a first barrier substantially preventing liquid flowand transporting ions only of the same charge as said first ions,

(b) providing a source of second ions of opposite charge to said firstions adjacent an aqueous liquid in a second zone comprising ion exchangemedium having exchangeable ions of the same charge as said second ions,said second ion source and second zone being separated by a secondbarrier substantially preventing liquid flow and transporting ions ofonly of the same charge as said second ions, said first and second ionsbeing selected from the groups consisting of (1) acid-forming ions orbase-forming cations or (2) hydroxide or hydronium ions of oppositecharge to (1), so that said first barrier passes ions of groups (1) or(2) but not both and the second barrier passes ions of opposite chargeto the first barrier, and

(c) applying an electrical potential through said first zone toelectrically charge the same with a charge opposite to that of ionstransported across said first barrier and through said second zone toelectrically charge the same with a charge opposite to the charge ofsaid first zone so that the ions transported across said first andsecond barriers into the ion exchange medium in said first and secondzones combine therein to generate an acid or a base in the aqueoussolutions therein.

In a further embodiment, an apparatus is provided for generating anacid, base or salt-containing aqueous solution comprising:

(a) a source of first ions adjacent an aqueous liquid in a first acid orbase generation zone, said first reservoir and first zone beingseparated by a first barrier portion substantially preventing liquidflow through the first barrier portion and transporting ions only of thesame charge as said first ions,

(b) a source of second ions of opposite charge to said first ionsadjacent an aqueous liquid in a second acid or base generation zone,said second ion source and second zone being separated by a secondbarrier portion substantially preventing liquid flow through the secondbarrier portion and transporting ions only of the same charge as saidsecond ions, and

(c) a first electrode in electrical communication with said first zoneand a second electrode in electrical communication with said secondzone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-8, 15-18 and 20-22 are schematic representations of apparatusaccording to the present invention.

FIGS. 9-14 and 19 are graphical representations of experimental resultsusing methods according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates to the apparatus and method for generating highpurity solutions of salts or acids or bases for use as chromatographiceluents. In ion chromatographic separations with suppressed conductivitydetection, dilute solutions of alkali carbonate and bicarbonate (e.g.,K₂CO₃, Na₂CO₃, and NaHCO₃) are often used as the eluents. Forsimplicity, the present invention first will be described with respectto the generation of alkali metal carbonate solutions. The inventionalso applies to the generation of other salt solutions, acids or basesas described later.

In one embodiment of the present invention, a salt containing aqueoussolution, e.g., K₂CO₃, is generated according to the following generalscheme. An aqueous solution including a source of first ions, e.g., K⁺ions, is disposed in the reservoir adjacent to a flowing aqueous liquidin a first acid or base generation chamber. A barrier substantiallypreventing liquid flow separates the source of first ions whiletransporting ions only of the same charge as the first ions. An aqueoussolution including a source of second ions, e.g., CO₃ ²⁻, of oppositecharge to the first ions also is disposed in the reservoir adjacent toan aqueous liquid solution in a second acid or base generation chamber.The second ion source and the second chamber are separated by a secondbarrier substantially preventing liquid flow while transporting ionsonly the same charge as the second ions. An electrical potential isapplied between the first chamber and the second chamber across thereservoir so that hydroxide ions are generated in one of the chambersand hydronium ions are generated in the other one. The cations andanions transported across the barriers combine with the hydroxide orhydronium ions, respectively, in the base and acid generator chamber togenerate an acid and base. Then, the generated acid and base solutionsare mixed in one of the chambers to form a salt containing solution.

Referring to FIG. 1, a block diagram of one form of generator of theforegoing type is illustrated. It will be described with respect to thegeneration of a pure K₂CO₃ aqueous solution from a source of that saltin an electrolyte reservoir within the generator. In this instance, thesource of both ions is contained in a single reservoir. Referring to thedrawing, the salt generator is contained within a housing 10 in which anaqueous solution of the salt 12 is maintained in central reservoir 14.Opposite ends of the solution 12 in reservoir 14 are in contact withoppositely charged first and second barriers 16 and 18 whichsubstantially prevent bulk liquid flow but transport ions only of theopposite charge as the barriers. As illustrated in FIG. 1, the barriersare independent of each other. However, as illustrated hereinafter, thefirst and second barrier may be replaced by a single continuous barrierwith segments of opposite charge. Base and acid generation first andsecond zones, illustrated in first and second chambers 20 and 22,respectively, are separated from chamber 14 by cation and anion exchangebarriers 16 and 18, respectively. Electrodes 24 and 26 are disposed inchambers 20 and 22, respectively. A source of an aqueous liquid 28,preferably deionized water, is directed by a pump, not shown, throughline 30 into chamber 20 where a solution of KOH is formed and from therein line 32 through chamber 22 and out through line 34 in the form of anaqueous salt eluent solution. In another embodiment illustratedhereinafter, the zones are disposed in one chamber. For simplicity ofdescription, the zones will be described in separate chambers unlessotherwise specified.

In the illustrated embodiment, electrode 24 is a cathode and chamber 20is a cathode chamber, while electrode 26 is an anode and chamber 22 isan anode chamber. Electrodes 24 and 26 are connected to a suitable powersupply, not shown, to complete the circuit. The positively chargedpotassium ions electromigrate through barrier 16 toward cathode 24forming KOH which is directed in line 32 to anode chamber 22. The anion,carbonate, electromigrates across ion exchange barrier 18 toward anode22 in which carbonic acid is formed by electrolysis. The base in line 32is mixed in chamber 22 with the formed acid, in turn to form the K₂CO₃eluent.

The form of the anode and cathode chambers, the anodes and cathodes, andthe barriers reservoir and chamber sizes, concentrations and volumes ofreagents, together with the conditions for electrolytic generation ofthe H₂CO₃ and KOH in the chambers are as generally described in U.S.Pat. No. 6,225,129. Also, as described in that application, control ofconcentration of the salt may be accomplished by a feedback loop.

The salt (e.g., K₂CO₃) solution 12 may be at a suitable concentration toprovide the corresponding desired maximum concentration of ionstransporting across barriers 16 and 18, respectively. The concentrationmay be controlled by varying the current as applied to the electrodes.As illustrated, the salt solution 12 is in direct contact with bothbarriers 16 and 18. A suitable concentration is on the order of 1 to 5 MK₂CO₃ with a volume sufficient to provide a reservoir of the K⁺ ions andCO₃ ²⁻ ions for generating the salt over an extended period of time(e.g., at least about 100 hours).

In one mode of operation of the apparatus of FIG. 1, the K₂CO₃ eluentgenerator, deionized water is pumped into the cathode chamber, and a DCcurrent is applied to the device. Under the applied electrical field, K⁺ions migrate from the electrolyte chamber into the cathode chamber andcombine with hydroxide ions produced through the reduction of water atthe cathode to form a KOH solution. The KOH solution along with hydrogengas (an electrolysis product) then flows through the anode chamber whereKOH combines with H₂CO₃ formed in the anode chamber (and anotherelectrolysis product, oxygen gas) to produce a K₂CO₃ solution. The K₂CO₃solution and the electrolysis gases (i.e., hydrogen and oxygen gases)are then passed through a degas tubing assembly (not shown) wherein theelectrolysis gases are removed. The K₂CO₃ solution is ready to be usedas an eluent in an ion chromatography system as illustrated in FIG. 2.The concentration of K₂CO₃ generated is directly proportional to theapplied current and inversely proportional to the flow rate of deionizedwater. In addition to the use of deionized water as the carrier,solutions of other reagents such as KOH may be used as the carriers forthe device. A mixture of such aqueous solutions andelectrolytically-inactive organic solvents may also be used as thecarrier.

While not specifically disclosed, an ion exchange resin bed orequivalent may be disposed in chamber 14 in the form of a mixed resinbed (e.g., comprising a cation exchange resin with exchangeable K⁺ ionsand an anion exchange resin with exchangeable carbonate ions) for thepurpose of supplying cations and anions to the eluent generator.

The nature of the cations and anions used as the source solution 12 maybe of the type described in the last named patent. Thus, suitablecations include metal ions such as alkali and alkaline earth metal ionsand suitable anions include organic or inorganic anions such asmethanesulfonic acid (MSA), carbonate and sulfate.

Referring to FIG. 2, an ion chromatography system is illustratedutilizing a salt generating cartridge of a similar type to that ofFIG. 1. In this instance, the deionized water flows through the anodechamber and the eluent salt solution is formed in the effluent from thecathode chamber, the reverse order of the flow system of FIG. 1.

Referring specifically to FIG. 2, housing 36 contains a source of anionsand cations in a salt solution 40 in reservoir chamber 42 in contact atopposite sides with a cation exchange barrier 44 and an anion exchangebarrier 46, respectively. To the outside of the barriers are cathodechamber 48 and anode chamber 50 in which are disposed cathode 52 andanode 54 connected to a power source, not shown. An aqueous liquidsource in the form of reservoir 56 flows through line 58 and throughanode chamber 50 in which acid is formed by electrolysis. From there,the acid flows through line 60 to cathode chamber 48 in which a base isformed by electrolysis. The base mixes with the acid from line 60 toform the electrolyte salt solution which exits in line 62. Electrolysisgases (i.e., hydrogen and oxygen gases) can be passed through a degastubing assembly 64 of the type described in the aforementioned patentapplication wherein the electrolysis gases are substantially removed.The K₂CO₃ salt solution can then be used in a chromatography system,such as an ion chromatography system as illustrated in FIG. 2. In thisinstance, the K₂CO₃ eluent solution flows in line 66 past a sampleinjector 68 and through anion separation column 70, suitably achromatography column of the type described in the aforementioned U.S.Pat. No. 6,225,129. The effluent from the chromatography column can bedetected directly or, as illustrated, flow in line 72 through membranesuppressor 74 and through line 76 to a detector 78, suitably aconductivity detector. In the illustrated embodiment, the suppressor maybe of the type sold by Dionex Corporation under the trademark SRS7 inwhich the effluent from the conductivity detector flows in line 80 to berecycled as a source of regenerant solution to the suppressor. The formof suppressor is described in U.S. Pat. No. 5,352,360.

In another embodiment of the invention illustrated in FIG. 3,independent reservoirs of anions and cations are used to form acids andbases, respectively, for mixing into the salt eluent of the presentinvention. As illustrated, a source of anion is disposed in a cathodereservoir 90 in the form of a K₂CO₃ salt solution 92 which is in contactwith a barrier 94 which passes anions but not cations and which blocksbulk liquid flow, similar to barrier 16 in FIG. 1. An ion exchange resinbed 96 is disposed in acid generation chamber 98 separated by barrier 94from the solution in reservoir 90.

Similarly, reservoir 100 contain solution 102 of a cation source whichmay also be in the form of K₂CO₃ salt solution separated by barrier 104from cation exchange resin bed 106 in base generation chamber 108disposed adjacent to acid generation chamber 98 at interface 110, inionic contact, typically in direct physical contact. The structure andelectrolytic reactions which take place in the acid generation and basegeneration sides of the system are similar to those set forth above withrespect to FIG. 1. In the illustrated embodiment, cathode 112 isdisposed in electrical communication with the solution 92 in reservoir90 while anode 114 is disposed in electrical communication with theanion source solution 100 in reservoir 102. As illustrated, cathode 112and anode 114 are disposed in direct contact with the reservoirssolutions and connected to a power source, not shown. Anions (carbonateions) in reservoir 90 migrate across barrier 94 into generation chamber98 toward anode 114. Similarly, cations (K⁺ ions) in reservoir 100 passthrough barrier 104 into chamber 106 toward cathode 112. K⁺ ionscombined with CO₃ ²⁻ ions at interface 110 to form a K₂CO₃ salt solutionin the K₂CO₃ generation column. As illustrated, water from source 116flows through interface 110 to carry out the K₂CO₃ salt solution instream 112. Similar sizes of the two reservoirs and concentrations ofsolution and operating conditions as described in U.S. Pat. No.6,225,129 can be used in this two reservoir system. The concentration ofKOH in the base generation column is directly proportional to theapplied current and inversely proportional to the flow rate. In thegeneration of K₂CO₃ eluent, KOH is not formed in the cation exchange bedwhich serves to carry K⁺ ions to interface 110.

In an embodiment, not shown, the charges in the anode and cathodechambers may be reversed together with the exchangeable ion charges onthe barriers and ion exchange resin beds. In this instance, the base isformed in the chamber on the left side of FIG. 3 and is carried by theflowing aqueous stream into the acid formed on the downstream chamber ofion exchange resin.

Also, if desired, the ion exchange beds in the acid or base generationchamber may be formed using ion exchange resins or other materials suchas described in U.S. Pat. No. 6,225,129.

In another embodiment not shown, the solutions in the cathode and anodereservoirs may be acids or bases rather than salts so long as the ionwhich passes through the barriers is present in the respective ionsource solutions. Thus, for example, the solution in the cathodereservoir may comprise H₂CO₃ and the solution in the anode chamber maycomprise a KOH.

Referring to FIG. 4, another embodiment of the invention similar to thatof FIG. 3 is illustrated with the exception that the ion exchange bedsin the acid and base generation chamber contact each other at aninterface which is substantially parallel to rather than transverse tothe flow of water from source 116. Like parts in FIGS. 3 and 4 aredesignated with like numbers. One advantage of this system is that thereis increased contact between the cation exchange resin bed and the anionexchange resin bed which can lead to lower device resistance.

In the embodiments of FIGS. 3 and 4, both the cathode and anodes areplaced outside of the acid or base generation stream and, thus, the saltgeneration stream. Because of this placement, the salt solution is freeof electrolysis gases. Thus, the use of a somewhat costly degas tubeassembly described in FIG. 2 for removing electrolysis gases may beavoided.

Another advantage of the embodiments of FIGS. 3 and 4 is that the samedevices used to generate a salt as described above may be used togenerate an acid or base eluent by choosing the appropriate electrolytesolution. By way of example of the foregoing principle, the system ofFIG. 4 may be used as a large capacity base generator by using a sourceof potassium in the anode chamber as described above in the form of, forexample, potassium hydroxide or potassium salt. However, in the cathodechamber, instead of using a salt or an acid of an ion which passesthrough the barrier, the same base solution may be used in the cathodeand anode reservoirs. For example, 4.0 M KOH solution may be used inboth reservoirs. In this manner, the cation in the anode reservoirpasses through the barrier into the cation exchange resin whilehydroxide electrolytically generated from water in the cathode chamberpasses to the anion exchange resin bed in the base generation chamber.K⁺ ions combine with hydroxide ions at the interface of the cationexchange bed and anion exchange bed to form a KOH solution in thecarrier stream. The concentration of the KOH generated is directlyproportional to the applied current and inversely proportional to theflow rate.

In another embodiment using the general configuration of FIG. 4, thesystem may be used as a large capacity acid generator. For example, itcould be used to generate methanesulfonic acid (MSA) as the electrolytesolution. In the acid generator embodiment, the polarities are reversedso that the first reservoir is a cathode generator and the secondreservoir is an anode reservoir. Also, the barrier for the firstreservoir is an anion exchange barrier and the first generator includesan anion exchange bed. Similarly, the second reservoir is an anodereservoir separated from cation exchange bed in the second generationchamber by a cation exchange barrier. The ionized water is pumped intothe MSA generation chamber and a DC current is applied between the anodeand cathode. Under the applied field, H⁺ ions in the anode reservoirmigrate across the cation exchange barrier into the cation exchange bed,and MSA⁻ ions in the cathode reservoir migrate across the anion exchangebarrier into the anion exchange bed. H⁺ ions combine with MSA⁻ ions atthe interface of the cation exchange bed and the anion exchange bed toform the acid, MSA solution. The concentration of MSA generated isdirectly proportional to the applied current and inversely proportionalto the flow rate.

FIG. 5 illustrates a dual-reservoir variation of the large capacity saltgenerator of FIG. 3 is illustrated. Like parts will be designated withlike numbers. In this embodiment, electrodes are disposed in or adjacentto the acid and base generation chambers which are isolated from eachother. Thus, the electrical circuit is between the electrode in thereservoirs and the oppositely charged electrodes in the acid and basegeneration chambers, respectively. The two generators can operate in thesame general manner as the acid and base generators of theaforementioned patent application in which the acid or base generated inthe first acid or base generation chamber is directed in a line to thesecond acid or base generation chamber to form a salt.

Referring specifically to FIG. 5, first electrolyte reservoir 120contains a source of cation, e.g., K⁺ ion, in a solution 122 in the formof a base, e.g., KOH, or a potassium salt. An anode 124 is disposed inreservoir 120 in contact with solution 122 which is also in contact withbarrier 126 in the cation exchange form which transports cations but notanions to base generation chamber 128. A cathode 130 is disposed in orin electrical communication with base generation chamber 128. Thecations migrate across barrier 126 to electrolytically form a base inbase generation chamber 128. The base is carried by water from source132 through line 134 to the acid generation chamber 136 describedhereinafter. The configuration and principles and parameters ofoperation of the base generation chamber are the same as those disclosedin U.S. Pat. No. 6,225,129.

A second electrolyte reservoir 140 contains a solution of anions whichare used to form a salt with the base flowing in line 134 to chamber136. A cathode 144 is disposed in the solution 142 of anions. To form acommon eluent salt for chromatography, the anions may be a mixture ofHCO₃/CO₃ ²⁻. In a manner analogous to the cation source reservoirs,these anions may be in a salt form or acid form. The bottom of reservoir140 is in open communication with anion exchange barrier 146 which is influid communication with acid generation chamber 136 in which anode 148is disposed.

The salt solution formed in chamber 136 flows out line 150 for use as aneluent. The principles of operation of this acid generation section areanalogous to the acid generation system described in the last named U.S.patent.

If desired, both electrolyte reservoirs may be filled with a salt, e.g.,K₂CO₃, as the electrolyte solution. In operation, the ionized water ispumped into the base generation chamber 128 in which KOH solution iselectrolytically generated. This base then passes through the acidgeneration chamber in which H₂CO₃ is generated. The acid and base aregenerated electrolytically and mixed to form K₂CO₃ eluent. The devicesuse two DC power supplies to control the current applied to the acid andbase generators 128 and 136, respectively. Since the power supplies areindependent, the system is capable of generating differentconcentrations of KOH and H₂CO₃, and thus the system is capable ofgenerating a combination of carbonate and bicarbonate at differentconcentrations in the eluent. A degas tubing assembly may be placedafter the chamber 136 to remove generated electrolysis gases (hydrogenand oxygen).

Referring to FIG. 6, another embodiment of the invention is illustratedusing certain principles of a non-integrated ion reflux device forgenerating an eluent as disclosed in U.S. patent application Ser. No.09/612,113, filed Jul. 7, 2000. In essence, the system includes inseries an acid and a base generation device of the type disclosed in thelast named patent application in series to combine the acid and basegenerated to form a salt which is used as the eluent for chromatography.

One embodiment of the invention is illustrated using an eluent generatorof the type described with respect to FIG. 3 of Ser. No. 09/612,113 incombination with a suppressor of the self-regenerating type described inU.S. Pat. No. 5,248,426. Referring to FIG. 3 of that application, amembrane suppressor is illustrated in which effluent from chromatographyseparator 160 in the form of an anion resin bed separation column passesthrough the chromatography effluent compartment 164 of sandwich membranesuppressor 166. In this instance, the chromatography effluentcompartment is sandwiched between two detector effluent compartments 168and 170 separated therefrom by cation exchange membranes 172 and 174,respectively. The structure of the membrane suppressor, which may be ofthe type disclosed in U.S. Pat. No. 5,352,360, may include ionconducting materials, not shown, placed in any of the compartments 164,168 or 170 to improve the current efficiency of the device. Anelectrical potential is applied across the flow path through sandwichsuppressor 166, suitably by flat plate electrodes 175 and 177 disposedat the outside of the detector effluent compartments as described in theabove patent.

The suppressor effluent flows through line 176 to conductivity cell 178for recycle in line 180 back to detector effluent compartments 168 and170 serving as the flowing aqueous stream for the generation of a saltfor the suppression of the eluent in the chromatography effluent flowinginto the suppressor in line 162. Details of operation of this type ofrecycle suppressor to accomplish these objectives is described in U.S.Pat. No. 5,350,360. The effluent from suppressor 116 containing a saltflows through line 182 to an acid generator and eventually to a basegenerator, both of the types described in U.S. patent application Ser.No. 09/612,174. Conduit 182 is provided to direct the salt stream fromsuppressor 166 to the inlet of eluent generator 184. This systemoperates substantially the same as the base generator described withrespect to FIG. 3 of the last named patent application. It includes asuitable housing 186 containing an electrolyte ion reservoir in the formof a packed bed of ion exchange resin 188. Resin bed 188 is separatedfrom a first generator electrode chamber 190 by a charged generatorbarrier 192 which prevents significant liquid flow but permits transportof electrolyte ions, in this instance anions, analogous to the barriersdescribed herein. An acid generation electrode (anode) 194 is disposedin acid generation electrode chamber 190. At the opposite end of barrier160 from electrode 194 is a flow-through electrode (cathode) 196.

For the analysis of anions, acid is generated in acid generator 184 formixing with the base generated by a second generator to be described,forming a salt. The line X-X separates the inlet section 188 a from theoutlet section 188 b of resin bed 188. The stream from suppressor 168 inline 182 flows into inlet section 188 a in salt form so that the resinis in CO₃ ²⁻ form while the outlet section is in the hydroxide ion form.The aqueous stream exits acid generator 184 through electrode 196 andexits the resin bed in line 198. The exiting solution in conduit 198 isdirected to a base generator 200 with a resin and components of oppositepolarity to acid generator 184. There, the resin bed 202 is in thecation (potassium) form to the left of line Y-Y while the bed to theright of line Y-Y is in hydronium ion form. The solution flows throughthe bed and exits through electrode 207 through line 204 to waste. Resinbed 202 is separated by cation exchange barrier 204 from that basegeneration chamber 206 containing cathode 208. The deionized water fromsource 210 flows through chamber 206 to carry the base generated thereinto acid generation chamber 190 which they are mixed to form an aqueoussalt solution. The salt solution flows through line 212 to a degas tubeat 214 of the type described above and from there to a sample injector216 to serve as the eluent which carries the liquid sample to anionseparator column 160. If desired, all of the foregoing polarities may bereversed so that eluent generator 184 generates base and eluentgenerator 200 generates acid.

In operation, deionized water is pumped into the KOH generation chamberin which the KOH solution is electrolytically generated and then flowsto the acid generation chamber in which the base combines with the acidwhich is electrolytically generated to form a salt (potassium carbonate)eluent. The device uses two DC power supplies to control the currentsthat are independently applied to the acid and base generation chambersso that combinations of carbonate and bicarbonate at differentconcentrations may be generated. To avoid ion contamination fromsamples, a high capacity cation exchange trap column, e.g., in K⁺ form,and a high capacity anion exchange trap column, e.g., in carbonate form,not shown, can be placed in line 182.

Referring to FIG. 7, another embodiment of the invention based on anon-integrated ion reflux device is illustrated similar to the device ofFIG. 6. From the point at which the component ions of the salt eluentgenerated is recycled from the suppressor effluent, the system of FIG. 6is the same as that of FIG. 7. Thus, like parts will be designated withlike numbers in the above descriptions of such components areincorporated at this point by reference. Like the embodiment of FIG. 6,FIG. 7 illustrates a system in which acid is electrolyticallyregenerated in an acid generation chamber, the base is generated in abase generation chamber and the regenerated acids and bases are mixed toform the chromatography eluent. In this embodiment, the recycledeffluent in line 182 from suppressor 112 only flows through the basegeneration unit while the acid generation unit operates with an anionsource solution in a substantially non-flowing reservoir which can bereplenished.

The base generation unit 200 is of the same configuration ascorresponding unit 200 of FIG. 6. In this instance, the salt solution inrecycle line 162 flows directly into and through the resin bed 200 andout porous anode 207 from left to right as illustrated.

As the device of FIG. 6, the deionized water from source 210 flowsthrough the base generation chamber 206 in which base (e.g., KOH) iselectrolytically generated. This generated base is carried in deionizedwater from source 210 into the acid generation unit 220 which includes ahousing 222 and a reservoir 224 of an aqueous solution of an anionsource such as a salt (e.g., K₂CO₃) or acid (carbonate acid). On oneside of reservoir 224 is an anion exchange barrier 226 which selectivelypasses anions but blocks bulk liquid flow to acid generation chamber 228in which is disposed anode 230. At the opposite end of reservoir 224,from barrier 226 is a cathode 232. The principle of operation of unit220 in isolation is the same as that described with respect to FIG. 1 ofU.S. Pat. No. 6,225,129. In this instance, reservoir 224 is the anionsource that electromigrates across barrier 226 toward anode 230 to formthe acid solution.

In operation, the deionized water is pumped from source 210 into thebase generation chamber 208 in which a base is electrolyticallygenerated. A KOH solution passes through acid generation chamber 228 inwhich acid is electrolytically regenerated to form a potassium carbonatesalt. The device uses two DC power supplies to control the currentswhich are independently applied. Thus, the device is capable ofgenerating KOH and H₂CO₃ at different concentrations and thus generatingcombinations of carbonate and bicarbonate at different concentrations inthe eluents.

In contrast to the system of FIG. 6, in FIG. 7 only the cations (e.g.,potassium ions) are recycled. Such recycle is accomplished by passingthe regenerant effluent from the electrolytic suppressor in line 182through the cation exchange resin bed 200 to the base generation unit.The anions (carbonate ions) are not recycled.

FIG. 8 illustrates another embodiment of the invention in which includesan integrated combination suppressor and acid or base generator of thetype described with respect to various embodiments of U.S. Pat. No.6,027,643. Like parts to those of FIG. 7 will be designated with likenumbers. This specific form of combination is illustrated with respectto FIG. 11 of that patent. In this instance, for anion analysis, a baseis generated by the combination suppressor/base generator for directionto an acid generator/salt mixing unit of the type illustrated undernumeral 220 of FIG. 7.

In operation, the effluent in line 212 flows through degas tubing 214 tothe sample injector 216 serving as the eluent to carry the samplethrough separation column 160 and line 182 to combinationsuppressor/eluent generator 250. Stream 182 passes through an ionexchange bed 252 including an upstream portion 252 a in cation (K⁺) formadjacent at line X-X to a downstream portion 252 b in the hydrogen ionform. An ion exchange barrier 254 is in contact with resin bed 252 andwith a resin bridge 256 between barrier 254 and flow-through cathode 258at the outlet end of cathode chamber 260 in which a base (KOH) iselectrolytically generated. The structure and principles of operation ofthis combination suppressor/eluent generator is described fully in U.S.Pat. No. 6,027,643. As described, the system can also be used for cationanalysis in which the resin in the suppressor is in anion form. Also,the other embodiments of the combination suppressor/eluent generatordisclosed in that patent may also be employed. Moreover, as disclosed inthat patent, a restrictor 262 is preferably used at the outlet of theconductivity detector for reasons disclosed in that patent.

Water from source 263 carries the aqueous base solution formed incathode chamber 260 flows in line 264 to anode chamber 228 and whichacid is electrolytically generated as described above. The acid and baseare mixed to form an eluent salt which flows in line 212, also asdescribed above.

As with the embodiment of FIG. 7, the device uses two DC power suppliesto control currents that are independently applied to the acid and basegenerator portions of the system. Thus, this system is capable ofgenerating any combination of carbonate and bicarbonate at differentconcentrations in the eluent.

Referring to FIG. 15, another embodiment of the invention is illustratedusing electrolytic device similar to that of FIG. 1 for simultaneousgeneration of base and acid solutions. Like parts will be designatedwith like numbers. One difference between the two devices is that thereis no conduit connecting the output from cathode chamber 24 and theanode chamber 22. Instead, deionized water flows through anode chamber26 to generate an acid solution.

As illustrated, the salt in electrolyte reservoir 12 is potassiummethanesulfonate (KMSA) rather than K₂CO₃ because methanesulfonic acid(MSA) is a common acid used as an eluent in chromatography. Asillustrated, a source of deionized water flows through acid generatorchamber 22 and the acid generated in that chamber flows out of thesystem in line 272, suitable for use as a chromatography eluent. Ifdesired, deionized water from sources 28 and 270 may be supplied from asingle source, not shown. The base (KOH) flows out of the system in line274 and is suitable for use a chromatography eluent for the separationof anions. Overall, the principle of operation of the salt generator ofFIG. 1 and the simultaneous acid and base generator of FIG. 15 are thesame with the exception that the acid and base is generatedindependently and not mixed. Thus, referring to FIG. 2, the generatedsalt would flow through a degassed tubing 64, sample injector 68, anionexchange separation column 70, anion suppressor 74 and conductivitydetector 78. Similarly, the base stream in line 274 can flow through asimilar system using the KOH as an eluent for anion chromatography. Inlike manner, MSA in line 272 can flow through an independent ionchromatography system with the exception that the separation column is acation separation column rather than an anion separation column and thesuppressor is a cation suppressor rather than an anion suppressor.

FIG. 16 illustrates a single reservoir salt generator which is similarin principle to the salt generator of FIG. 3. However, it requires onlya single electrolyte reservoir and high pressure eluent generationchamber and uses an integral barrier containing adjacent anionic andcationic functionality which may be in the form of adjacent stacks ofion exchange membranes of opposite polarity. As illustrated, the highpressure eluent generation chamber contains both the anode and thecathode.

Referring specifically to FIG. 16, a block diagram of one form ofgenerator of this type is illustrated. It will be described with respectto the generation of a K₂CO₃ aqueous solution from a source of that saltin an electrolytic reservoir within the generator. The generator iscontained within a housing 280 in which an aqueous solution of the salt282 is maintained in reservoir 284. One end of the solution reservoir284 is in contact with a continuous charged barrier 286 whichsubstantially prevents bulk liquid flow but which transports ions onlyof the opposite charge as the charged barrier portions adjacent to thesolution 282 and reservoir 284. As illustrated, barrier 286 includes twobarrier portions 286 a and 286 b which in composite form a continuousbarrier against liquid flow. Barrier portion 286 a has exchangeable ionsof positive charge which permit the passage of K⁺ ions but which blocksthe passage of CO₃ ⁻². Barrier portion 286 a is in contact with andintegral with barrier portion 286 b which passes negative ions such asCO₃ ⁻² but which blocks the flow of K⁺ ions. In composite, barrierportions 286 a and 286 b block the flow of block bulk liquid flow fromreservoir 284 through barrier 286.

As illustrated, barrier 286 is formed of a series of stacked membraneswhich interleave with each other so that the positively charged membrane286 a extend between pairs of negatively charged membranes 286 b. Theoverlap assists sealing at high pressures against liquid leaks.Alternatively, other forms of positive and positively charged andnegatively charged barrier portions without interleaving may be used solong as there is a continuous path for the corresponding ions insolution 282 through the membranes and bulk liquid flow is blocked. Forexample, an inert plastic spacer may be used to separate the differentcharged barriers.

As illustrated, a high pressure eluent generator 288 is disposed on theopposite side of barrier 286 from reservoir 284. Adjacent barrierportion 286 a is cathode 290 while adjacent barrier portion 286 b isanode 292. The cathode and anodes may be of the type described above. Acontinuous fluid path is provided from inlet end 288 a to outlet end 288b of eluent generation chamber 288. An open space 288 c may be providedseparating cathode 290 and anode 292. Deionized water from a source 294flows through eluent generation chamber 288. A DC electrical current isapplied to the anode and cathode. Under the applied electric field,potassium ions in the electrolyte reservoir 284 migrate across the stackof cation exchange membranes of barrier portion 296 a and combine withthe hydroxide ions formed at the cathode by the reduction of water toform a KOH solution.

Simultaneously, carbonate ions migrate across the stack of anionexchange membranes in the form of barrier portion 286 b and combine withhydronium ions formed at anode 292 by the oxidation of water to form acarbonic acid solution. The potassium hydroxide solution reacts with thecarbonic acid solution to form a potassium carbonate solution in theregion of anode 292 which flows out outlet 288 b. The potassiumcarbonate may be used as an eluent in chromatography, e.g., in ionchromatography, as illustrated in the flow system of FIG. 2. Theconcentration of potassium carbonate formed is directly proportional tothe applied DC current and inversely proportional to the flow rate ofdeionized water pumped into the eluent generation chamber.

In another embodiment, illustrated in FIG. 17, a structure includingfeatures described in the embodiment of FIG. 16 can be used as a largecapacity acid or base generator. Like parts will be designated with likenumbers for FIGS. 16 and 17. As illustrated in FIG. 17, the solution inreservoir 284 is potassium hydroxide solution. Instead of disposing ananode in the eluent generation chamber, an anode 296 is disposed inreservoir 284. The electrical path is between anode 296 and cathode 290and K⁺ ions flow through the stack of positively charged membranes inbarrier portion 286 a. The device can be operated as a large capacityKOH eluent generator as described in U.S. Pat. No. 6,225,129.

In another embodiment shown in FIG. 18, the basic structure of FIG. 17may be used for generation of an acid, e.g., methanesulfonic acid (MSA)solution using the same solution as in reservoir 284. In this instance,the anode 292 is included in eluent generation chamber 288 and thecathode is eliminated from the chamber. Instead, the cathode is disposedin contact with the solution reservoir 284. The electrical path isbetween the cathode and anode through the barrier portion 286 b in theform of a stack of anion exchange membranes.

In another embodiment, after forming a salt-containing solution by anyof the foregoing methods using any of the foregoing types of apparatus,the solution is directed to an electrolytic pH modifier device in whichthe pH level of the salt-containing solution is modified. For example,the pH of an alkali metal salt of a weak acid would be raised to form asalt of a conjugate acid anion in a mixture with the weak acid anion.Examples of such modifications include partially converting the weakacid anions in K₂CO₃ or K₃PO₄ to one of their conjugate acid forms,H₂CO₃ or HCO₃ ⁻¹ or KHPO₄ ⁻² or KH₂PO₄ ⁻¹. The salt leaving the pHmodifier typically includes a mixture of the alkali metal weak acid saltand the alkali metal conjugate acid salt.

Referring to FIG. 20, one embodiment of salt-forming apparatus incombination with an electrolytic pH modifier is illustrated. In thisinstance, the salt is formed by a dual-ion exchange zone/singlereservoir salt-forming generator somewhat modified from such a generatorillustrated in FIG. 16. It will be described with respect to thegeneration of K₂CO₃ aqueous solution from a source of that salt in anelectrolytic reservoir within the generator. The generator is containedin a reservoir 300 in which an aqueous solution of the salt 302 ismaintained. One end of the salt solution 302 is in contact with a saltcharged barrier 306 which substantially prevents bulk liquid flow butwhich transports ions only of the opposite charge as the respectivelycharged barrier portion adjacent to the solution 302 in reservoir 300.As illustrated, barrier 306 includes two barrier portions 306 a and 306b separated by a plastic insulator 308 forming a composite continuousbarrier against bulk liquid flow. The barriers may be of the same typedescribed above. As illustrated, barrier portion 306 a includesexchangeable cations while barrier portion 306 b includes exchangeableanions so that potassium ions migrate through barrier portion 306 a andcarbonate ions migrate through barrier portion 306 b under the appliedelectric field. The plastic insulator extends across the length ofbarrier portions 306 a and 306 b and electrically isolates them fromeach other. Thus, barrier portion 306 a has exchangeable ions ofpositive charge which permit the passage of K⁺ ions but which blocks thepassage of CO₃ ⁻² ions. Likewise, barrier portion 306 b passes negativeions such as CO₃ ⁻² which blocks the flow of K⁺ ions.

As illustrated, a high pressure eluent generator 310 is disposed on theopposite side of barrier 306 from reservoir 304. Adjacent barrierportion 306 a is a cathode 312 disposed in a cation exchange resin bed313 while adjacent barrier portion 306 b is an anode 314 disposed in ananion exchange resin bed 315. A fluid path is provided through insulator308 in the form of a cut-out 316 or the like. The ionized water from asource 315 flows through eluent generator chamber 310. A DC electriccurrent is applied to the anode and cathode. Under the applied electricfield, potassium ions in the electrolytic reservoir 304 migrate acrossbarrier portion 306 a and combine with hydroxide ions forms at thecathode by the reduction of water to form a KOH solution.

Simultaneously, carbonate ions migrate across barrier portion 306 b andcombine with hydronium ions formed at anode 314 by the oxidation ofwater to form a carbonic acid solution. The potassium hydroxide solutionreacts with the carbonic acid solution to form a potassium carbonatesolution in the region of anode 314 which flows out in line 320.

Referring again to FIG. 20, the K₂CO₃ flows in line 320 to electrolyticpH modifying device 322 of the general type illustrated in U.S. Pat. No.6,225,129 which includes an aqueous solution 324 in a reservoir 326. Acathode 328 is disposed in solution 324. A charged barrier 330 is incontact with solution 324 which substantially prevents bulk liquid flowbut which transports ions only of the opposite charge as the chargedbarrier. For the transport of K⁺ ions as illustrated, barrier 330includes exchangeable cations. The salt in line 320 flows through pHmodifying flow channel 332 which contains flow-through cation resinexchange bed 334 in electrical communication with anode 336. By passinga DC current between cathode 328 and anode 336, a controlled amount ofhydronium ions displaces potassium ions in flow channel 332 to convert acontrolled amount of K₂CO₃ into KHCO₃ and thus generates acarbonate/bicarbonate eluent with the desired concentration ratio K₂CO₃to KHCO₃. Expressed generically, the carbonate salt is an acid and ispartially converted to the bicarbonate (conjugate acid), both in saltform. Other conversions of acid to conjugate acids can be accomplishedby the apparatus of the present invention where salts of weak acid suchas K₃PO₄.

In another embodiment illustrated in FIG. 21, the salt eluent generatoris of the same type as illustrated in FIG. 20. In this instance, the pHmodifying device 341 may be of the general type illustrated in U.S. Pat.No. 6,325,976 with the exception that the feed solution is K₂CO₃ andthat the ion exchange resin bed serves the function of pH modification,not suppression. Like parts will be designated with like numbers forFIGS. 20 and 21. As illustrated, the salt solution in line 320 flowsthrough ion exchange resin bed 340 contained within flow-through housing342. In this embodiment, the ion exchange resin 340 is a cation exchangeresin. The electrolytic pH modifier may be of the same general type asillustrated in FIG. 1 of U.S. Pat. No. 6,325,976. Thus, it includes abarrier 344 which separates bed 340 from an electrode 346 in a hollowhousing defining electrode chamber 348 preventing bulk liquid flow butpermitting transport of ions only of the same charge as the charge ofthe exchangeable ions in resin bed 340. In the illustrated system,barrier 344 is in the form of a cation exchange membrane or plug andelectrode 348 is a cathode. An aqueous solution from a source 350continuously flows through chamber 346. The salt in line 320 flowsthrough ion exchange bed 340, porous electrode 352 and out line 354 inthe form of a K₂CO₃/KHCO₃ solution. The principle of transportingpotassium ions across membrane 344 and simultaneously converting part ofthe salt of the weak acid to its bicarbonate form are the same asillustrated with respect to the embodiment of FIG. 20.

Referring to FIG. 22, another embodiment of the invention is illustratedsimilar to the embodiment of FIG. 21. Like parts will be designated withlike numbers. Thus, the salt conversion of the left-hand side of FIG. 22is the same. The principle difference is that the aqueous solution 350,suitably deionized water, flows through a second electrode chambercontaining the anode which then flows in line 360 back through electrodechamber 346. The cations, K⁺ as illustrated, pass through barrier 344 asillustrated in FIG. 21.

Referring again to FIG. 22, barrier 362 separates bed 340 from anode 364in the interior of electrode chamber 366. Barrier 362 is of the sametype as barrier 344 but includes exchangeable ions of opposite charge.The principles of electrolytic operation using a cathode and an anodeisolated from the ion exchange bed 340 is illustrated with respect toFIG. 2 of U.S. Pat. No. 6,027,643. The difference is that the bed 340serves as a pH adjuster rather than a suppressor as in the patent.

Other electrolytic or non-electrolytic pH adjusters may be used whichaccomplish the purposes of the present invention of converting a weakacid salt to its conjugate acid.

All of the above systems can be used to generate other acids (e.g.,sulfuric acid, methane sulfonic acid, acetic acid, etc.) or bases (e.g.,of alkali metals and alkaline earth) as set forth in the above patentsand applications and mixtures thereof to form salts. Further, thepolarity of any of the base generators may be reversed to reverse theorder of generation. Similarly, the order of flow through any acid orbase generator in a combination of different generators may be reversed.All of the above patents and applications are incorporated herein byreference. In addition to being used as eluents in ion chromatography,the high purity salt, acid, and base solutions generated as described inthis application may be used as eluents in liquid chromatography, andother chemical analysis applications such as titration, flow injectionanalysis, etc.

In order to further illustrate the present invention, the followingspecific examples are provided.

EXAMPLE 1

This example illustrates use of an eluent generator of the typeillustrated in FIG. 2 to generate K₂CO₃ in ion chromatographicseparation of anions.

A K₂CO₃ eluent generator of the type illustrated in FIG. 2 wasconstructed. An EGC-KOH generator cartridge (P/N 53986, DionexCorporation, Sunnyvale, Calif.) was used as the cathode chamber, and anEGC-MSA generator cartridge (P/N 53987, Dionex Corporation) was firstconverted to the carbonate form and used as the anode chamber. Thecathode chamber was connected to the anode chamber using a coupler (1inch in internal diameter and 3 inch in length) made of polypropylene.This polypropylene coupler serves as the electrolyte chamber of theK₂CO₃ generator was filled with about 50 mL of 3.0 M K₂CO₃ solution. ADionex EG40 Eluent Generator Module was used to supply the DC current tothe anode and cathode of the eluent generator. The K₂CO₃ generator wasoperated in the flow direction of cathode chamber (KOH generationchamber) to anode chamber (H₂CO₃ generation chamber). FIG. 2 illustratesan ion chromatographic system using the K₂CO₃ eluent generator. A DX500ion chromatographic system (Dionex Corporation) consisting of a GP40pump, an injection valve and an AS9 HC separation column (4-mmID×250-length) was used. A Dionex ASRS anion suppressor (P/N 53946) wasused as the suppressor. A built-in power supply in a Dionex ED40detector was used to supply 300 mA of DC current to the suppressor. ADionex ED40 conductivity detector equipped with a flow-throughconductivity cell was used as the detector. A Dionex PeakNet 5.0computer workstation was used for instrument control, data collectionand processing.

The operation of the K₂CO₃ eluent generator was evaluated by using it togenerate a 9.0-mM K₂CO₃ eluent (the applied current was 29 mA) at 1.0mL/min for separation of five common anions on a 4-mm AS9-HC column.FIG. 9 shows the chromatograms obtained using either 9 mM K₂CO₃ from abottle prepared by the conventional method or 9 mM K₂CO₃ generated usingthe K₂CO₃ eluent generator. The chromatogram obtained using the K₂CO₃eluent generator was similar to that obtained using 9.0 mM K₂CO₃prepared conventionally. In another set of experiments, the system shownin FIG. 2 was operated continuously to perform the separation of fivecommon anions for 15 days. FIG. 10 shows the stability of retentiontimes of five common anions over 850 runs performed during the test. Thepercent RSDs for retention times of five anions ranged from 0.5 percentfor fluoride to 2.2 percent for nitrate. These results indicate that theK₂CO₃ eluent generator is capable of generating the carbonate eluentreproducibly over an extended period of time.

In another set of experiments, the K₂CO₃ generator was programmed togenerate a linear gradient of 0 to 30 mM K₂CO₃ at 1.0 mL/min, and theconductance of the K₂CO₃ eluent generator was measured. It was foundthat the device flow direction had an effect on the conductance profileof the K₂CO₃ generated. FIG. 11 shows the conductance profiles of alinear K₂CO₃ gradient (0 to 30 mM at 1.0 mL/min) obtained using thedevice in both flow directions. The flow direction of cathode chamber toanode chamber yielded a better linear gradient profile.

EXAMPLE 2

This example illustrates use of the same apparatus as Example 1 togenerate a K₂CO₃/KHCO₃ eluent in ion chromatographic separation ofanions.

A K₂CO₃/KHCO₃ generator cartridge was constructed using the samecomponents that were used for the K₂CO₃ generator cartridge, asdescribed in Example 1. The electrolyte chamber of the K₂CO₃/KHCO₃eluent generator was filled with about 50 mL of 1.8 M K₂CO₃/1.7 M KHCO₃solution. The flow direction was from the cathode chamber to the anodechamber. A Dionex EG40 Eluent Generator Module was used to supply the DCcurrent to the anode and cathode of the eluent generator.

The performance of the K₂CO₃/KHCO₃ eluent generator was evaluated byusing it to generate a 1.8 mM K₂CO₃/1.7 mM KHCO₃ eluent at 2.0 mL/minfor separation of five common anions. An ion chromatography systemidentical to that used in Example 1 was used in the experiments exceptthat a 4-mm AS4A SC column (4-mm ID×250-length) was used as theseparation column. To generate 1.8 mM K₂CO₃/1.7 mM KHCO₃ eluent at 2.0mL/min, a DC current of 8.4 mA was applied to the K₂CO₃/KHCO₃ eluentgenerator cartridge. It was assumed that carbonate and bicarbonate wouldmigrate across the membranes in the anode chamber in a ratio similar tothat in the electrolyte solution. FIG. 12 shows a representativechromatogram obtained using the device.

EXAMPLE 3

This example illustrates the use of an eluent generator of the typeillustrated in FIG. 5 to generate a K₂CO₃ eluent in ion chromatographicseparation of anions.

A potassium carbonate eluent generator of the type illustrated in FIG. 5was constructed. An EGC-KOH cartridge (P/N 53986, Dionex Corporation,Sunnyvale, Calif.) was used as the KOH generator. The EGC-H₂CO₃cartridge was constructed using the same components as those used in anEGC-MSA generator cartridge (P/N 53987, Dionex Corporation), except thatthe ion exchange connector was in the carbonate form. The electrolytereservoir of the EGC-H₂CO₃ cartridge was filled with a solution of 3.0 MK₂CO₃. A Dionex EG40 Eluent Generator Module was used to supply andcontrol the DC current (33 mA) to the anode and cathode of the EGC-H₂CO₃cartridge. A Dionex SC20 DC power supply module (P/N 057755) was used tosupply and control the DC current (29 mA) to the anode and cathode ofthe EGC-KOH cartridge. The other components of the ion chromatographysystem were the same as those described in Example 1. The operation ofthe eluent generator was evaluated by using it to generate a 9.0-mMK₂CO₃ eluent at 1.0 mL/min. FIG. 13 shows the separation of seven commonanions on a 4-mm AS9-HC column (P/N 051786, Dionex Corporation) usingthe K₂CO₃ eluent generated.

EXAMPLE 4

This example illustrates the use of an eluent generator of the typeillustrated in FIG. 5 to generate a K₂CO₃/KHO₃ eluent in ionchromatographic separation of anions.

A potassium carbonate eluent generator of the type illustrated in FIG. 5was constructed. An EGC-KOH cartridge (P/N 53986, Dionex Corporation,Sunnyvale, Calif.) was used as the KOH generator. The EGC-H₂CO₃cartridge was constructed using the same components as those used in anEGC-MSA generator cartridge (P/N 53987, Dionex Corporation), except thatthe ion exchange connector was in the carbonate form. The electrolytereservoir of the EGC-H₂CO₃ cartridge was filled with a solution of 3.0 MK₂CO₃. A Dionex EG40 Eluent Generator Module was used to supply andcontrol the DC current (17.4 mA) to the anode and cathode of theEGC-H₂CO₃ cartridge. A Dionex SC20 DC power supply module (P/N 057755,Dionex Corporation) was used to supply and control the DC current (15.4mA) to the anode and cathode of the EGC-KOH cartridge. The othercomponents of the ion chromatography system were the same as thosedescribed in Example 1. The operation of the eluent generator wasevaluated by using it to generate an eluent of 3.5 mM K₂CO₃ and 1.0 mMKHCO₃ at 1.2 mL/min. FIG. 14 shows the separation of seven common anionson a 4-mm AS 14 column (P/N 046124, Dionex Corporation) using theK₂CO₃/KHCO₃ eluent generated.

EXAMPLE 5

In this example, the eluent generator of FIG. 16 is used in a typicalion chromatography system including the components downstream of thegenerator illustrated in FIG. 2. Specifically, seven ions were separatedon a Dionex AS9 HC column using the 9 mM potassium carbonate generatedby a device of FIG. 17. A DC current of 29 mA was applied to thecarbonate generator to generate 9 mM K₂CO₃ at 1.0 mL/min. The resultsare shown in FIG. 19.

EXAMPLE 6

In this example, the apparatus of FIG. 21 is used. The K₂CO₃ solution inline 20 is at a concentration of 9 mM at 1.0 mL/min. flow rate. A DCcurrent of 3.22 mA is applied to pH modifying device 341. To displace anamount of K+ ions equivalent to 2 mN K⁺ at 1.0 mL/min. The resultingsolution in line 354 contains 8.0 mM K₂CO₃ and 1.0 mM KHCO₃ at the sameflow rate.

1. A method of generating an acid and a base comprising the steps of:(a) providing a source of first ions adjacent an aqueous liquid in afirst acid or base generation zone, said first ion source and first zonebeing separated by a first barrier substantially preventing liquid flowand transporting ions only of the same charge as said first ions, (b)providing a source of second ions of opposite charge to said first ionsadjacent an aqueous liquid in a second acid or base generation zone,said second ion source and second zone being separated by a secondbarrier substantially preventing liquid flow and transporting ions onlyof the same charge as said second ions, and (c) transporting ions of afirst charge, positive or negative, across said first barrier byapplying an electrical potential through said first zone to electricallycharge the same with a charge opposite to said first charge and applyingan electrical potential through said second zone to electrically chargethe same with a charge opposite to the charge of said first zone so thathydroxide ions are generated in one of said first or second zones andhydronium ions are generated in the other of said first and second zonesand ions of opposite charge to the electrical charges of said first andsecond zones, respectively, are transported across said first and secondbarriers to combine with said hydroxide or hydronium ions in said firstand second zones to generate an acid-containing aqueous solution in oneof said first or second zones and a base-containing aqueous solution inthe other one.
 2. The method of claim 1 further comprising the step of:(d) mixing said generated acid-containing and base-containing aqueoussolutions to form a salt-containing aqueous solution.
 3. The method ofclaim 1 in which said first and second zones are in separate first andsecond chambers, respectively.
 4. The method of claim 1 in which thefirst and second ion sources comprise a salt solution of said first andsecond ions.
 5. The method of claim 4 in which said salt solution is inone chamber.
 6. The method of claim 4 in which said sources of saidfirst and second ion comprise a common reservoir of said salt solutiondisposed between said first and second barriers.
 7. The method of claim1 in which said first and second barriers are part of a continuousbarrier.
 8. The method of claim 1 in which said first and secondbarriers are independent of each other.
 9. The method of claim 1 inwhich said electrical potential is applied between first and secondelectrodes of opposite charge in electrical communication with saidfirst and second zones, respectively.
 10. The method of claim 9 in whichsaid first and second electrodes are in contact with said first andsecond zones, respectively.
 11. The method of claim 9 in which saidfirst electrode is in contact with said first ion source and said secondelectrode is in contact with said first zone,
 12. The method of claim 2in which said salt-containing aqueous solution flows as a chromatographyeluent together with a sample analyte solution through chromatographyseparation medium to chromatographically separate the analytes.
 13. Themethod of claim 1 in which said acid-containing aqueous solution flowsas a chromatography eluent together with a sample analyte solutionthrough chromatography separation medium to chromatographically separatethe analytes.
 14. The method of claim 1 in which said base-containingaqueous solution flows as a chromatography eluent together with a sampleanalyte solution through chromatography separation medium tochromatographically separate the analytes.
 15. The method of claim 2 inwhich an aqueous liquid flows through said first chamber and carries theacid or base generated therein to said second chamber wherein saidmixing takes place.
 16. The method of claim 1 in which said first andsecond ion sources comprise first and second substantially non-flowingsolutions of said first and second ions, respectively.
 17. The method ofclaim 1 in which said first and second ion sources comprise flowingsolutions.
 18. The method of claim 1 in which said first and second ionsources are selected from the group consisting of aqueous solutions ofan acid, a base or a salt.
 19. The method of claim 1 in which said firstand second zones comprise ion exchange medium of opposite chargeadjacent to said first and second barriers.
 20. The method of claim 1 inwhich said first and second ion sources are contained in separate firstand second reservoirs, respectively.
 21. The method of claim 20 in whichone of said first or second ion source reservoirs comprises asubstantially non-flowing solution comprising said first or second ionsand the other of said first or second ion source reservoirs comprisesliquid flow-through ion exchange medium having exchangeable ionscomprising the other of said first and second ions.
 22. The method ofclaim 2 in which said first ion source comprises first reservoir ionexchange flow-through medium disposed in a first reservoir and havingexchangeable first ions and in which a solution of said first ions flowsthrough said first reservoir ion exchange medium.
 23. The method ofclaim 22 in which an analyte sample and said salt-containing aqueoussolution flow through chromatography separation medium and then througha chromatography effluent flow channel of a membrane suppressorseparated by a suppressor membrane from a regenerant flow channel, saidmethod further comprising forming a solution comprising said first ionsin said regenerant flow channel which flows through said first reservoirion exchange resin.
 24. The method of claim 21 in which said second ionsource comprises ion exchange medium disposed in a second reservoir, andthe ion solution formed in said regenerant flow channel is a salt ofsaid first and second ions, said method further comprising flowing saidformed salt through said second reservoir.
 25. The method of claim 24 inwhich said electrical potential is applied across said second reservoirion exchange medium, said method further comprising flowing said formedsalt solution past an electrode adjacent the outlet of second ionexchange medium of opposite charge to the charge of said second chamberso that said first ions electromigrate toward said electrode.
 26. Themethod of claim 25 in which the first ion-containing solution flowingout of said first reservoir flows through said second reservoir ionexchange medium having exchange ions of the same charge as said firstion solution in a first reservoir comprising said first ion source. 27.The method of claim 2 in which said first ion source comprises a firstion source reservoir and said second ion source comprises a second ionsource reservoir, said method further comprising: (e) flowing saidformed salt-containing solution as an eluent with analyte sample throughchromatographic separation medium, and (f) flowing the chromatographyeffluent through a suppressor comprising ion exchange medium havingexchangeable ions of the same charge as said first ions.
 28. The methodof claim 1 in which a first electrical potential is applied between afirst pair of electrodes of opposite charge, one of which is inelectrical communication with said first reservoir and the other ofwhich is in electrical communication with said first zone, and a secondelectrical potential is applied between a second pair of electrodes ofopposite charge, one of which is in electrical communication with saidsecond reservoir and the other of which is in electrical communicationwith said second zone.
 29. The method of claim 2 further comprising thestep of (e) electrolytically modifying the pH value of saidsalt-containing solution.
 30. The method of claim 29 in which the anionof the salt in said salt-containing solution is a weak acid.
 31. Themethod of claim 30 in which said salt-containing solution is an alkalimetal carbonate and said electrolytically modified salt-containingsolution comprises an alkali metal carbonate/bicarbonate solution.
 32. Amethod of generating an acid or base-containing aqueous solutioncomprising the steps of: (a) providing a source of first ions adjacentan aqueous liquid in a first zone comprising ion exchange medium havingexchangeable ions of the same charge as said first ions, said first ionsource and first zone being separated by a first barrier substantiallypreventing liquid flow and transporting ions only of the same charge assaid first ions, (b) providing a source of second ions of oppositecharge to said first ions adjacent an aqueous liquid in a second zonecomprising ion exchange medium having exchangeable ions of the samecharge as said second ions, said second ion source and second zone beingseparated by a second barrier substantially preventing liquid flow andtransporting ions of only of the same charge as said second ions, saidfirst and second ions being selected from the groups consisting of (1)acid-forming ions or base-forming cations or (2) hydroxide or hydroniumions of opposite charge to (1), so that said first barrier passes ionsof groups (1) or (2) but not both and the second barrier passes ions ofopposite charge to the first barrier, and (c) applying an electricalpotential through said first zone to electrically charge the same with acharge opposite to that of ions transported across said first barrierand through said second zone to electrically charge the same with acharge opposite to the charge of said first zone so that the ionstransported across said first and second barriers into the ion exchangemedium in said first and second zones combine therein to generate anacid or a base in the aqueous solutions therein.
 33. The method of claim32 in which said first and second zones are in separate first and secondchambers, respectively.
 34. The method of claim 32 in which said firstand second zones are in one chamber.
 35. The method of claim 32 in whichsaid first and second ion sources are in first and second ionreservoirs, respectively.